1. Field of the Invention
This invention relates to devices for continuously excavating an elongated, substantially linear trench, and more particularly, to trench excavating machines of a mobile or portable character which function to propagate or project a trench forwardly of a vehicle supporting the cutting or excavating element of the apparatus.
2. Brief Description of the Prior Art
A number of machines have previously been provided for quickly and continuously excavating a trench or ditch, and have included a wheel-mounted vehicle carrying a cutting element which continuously bites into and removes earth for the purpose of projecting the trench in a desired direction. Generally, such machines are capable of continuous operation to continuously project the trench along a line desired. Many include teeth or buckets mounted on some form of endless chain which is driven in rotation to bring the buckets into contact with the earth at the leading end of the trench for biting and scraping away earth to enlarge and project the trench.
There have also been proposed and patented, various excavating machines which include a rotary-driven auger mounted at the front of some type of prime mover or conveyance mechanism, with the auger having a pilot bit or some sort of ground excavating device located at the lower end of the auger, with the auger functioning both to extend a trench and to elevate dirt from the trench to ground level. Patents of this type are those which are shown in Saumenig U.S. Pat. No. 3,443,326 and Nixon U.S. Pat. No. 814,982. Auger trench excavators mounted at the rear of the vehicle or prime mover are also shown in Fullard U.S. Pat. No. 785,302, Kessler U.S. Pat. No. 919,595, Stewart U.S. Pat. No. 202,200 and Swedish Pat. No. 155,459. A device of this sort is also shown in French Pat. No. 1,224,143 and in Berry U.S. Pat. No. 2,545,016.
It is necessary in all trench excavating machines of the type which utilize or depend upon a rotated auger or screw-type cutting member to cut away and lift the dirt, to support such cutting element at its lower end in some type of bearing or journal which will permit rotation of the screw or auger blade. To the extent that such journal or bearing offers resistance to the forward movement of the auger blade as the trench is extended horizontally in the earth, the efficiency of the machine is decreased and the expediency with which the trench may be extended and completed is reduced.
Bearings or journals of the type described have, in some instances, been mounted in flat supporting shoes or plates which are provided at their forward end with a sharp cutting edge. Two devices of this character are shown in Hanneborg U.S. Pat. No. 530,687 and Nixon U.S. Pat. No. 814,982. In the case of both of these machines, the broad expanse of the shoe, though reduced to a slight extent in its frictional resistance to movement through the earth by the formation of a cutting edge on the forward side thereof, nevertheless offers significant resistance to the advance of the auger into the earth at the forward side of the trench, and reduces the speed with which the trench can be dug and completed. Moreover, the helically turned blade of the auger, in each instance, terminates in a relatively blunt, substantially horizontal lower end, so that the cutting efficiency of the blade is reduced at this location.
In my U.S. pat. application Ser. No. 712,601, of which the present application constitutes a continuation-in-part, I have described an improved trench excavating machine which utilizes an auger assembly having a helically turned blade for the purpose of accomplishing the primary earth cutting and removal function of the apparatus. The helical blade is secured around an elongated shaft which is supported at its lower end in a bearing or journal which is positioned atop a keel structure located at the lower end of the blade. I have now determined that while the apparatus described in my co-pending parent application works well in practice, the efficiency with which the auger excavator can be projected through the earth is reduced due to the drag which is developed at the lower end of the auger at the auger-keel connection. It is with respect to this structure that the present invention constitutes an improvement.